Sang-Hyun Yun

Perpendicular lamellae induced at the interface of neutral self-assembled monolayers in thin diblock copolymer films

Abstract We obtained perpendicular lamellar orientations in thin films of symmetric polystyrene- block -poly(methyl methacrylate), PS- b -PMMA, on self-assembled monolayers (SAMs) of 3-( p -methoxyphenyl)propyltrichlorosilane (MPTS) prepared on silicon wafers. In contrast to completely parallel lamellae on silicon wafers having a native oxide layer, perpendicular lamellae at the MPTS interface with parallel lamellae at the air interface were directly observed by transmission electron microscopy (TEM) in cross-sectional view. The perpendicular lamellae at the MPTS interface were attributed to the non-preferential (neutral) MPTS-covered substrate to both PS and PMMA blocks. The neutrality of the SAMs of MPTS was confirmed by the similar interfacial tension values of the SAMs of MPTS with PS and PMMA, estimated by contact angle measurements.

Micropatterning of a single layer of nanoparticles by lithographical methods with diblock copolymer micelles

We have demonstrated micropatterning of a single layer of nanoparticles by combining a self-assembly of diblock copolymer micelles with conventional and soft lithographical methods. On a photoresist micropattern fabricated by conventional photolithography, a single layer of diblock copolymer micelles containing precursors of nanoparticles was spin-coated. By plasma and lift-off processes, nanoparticles with the preservation of a pseudo-hexagonal order of micelles were synthesized in the micropattern without their aggregation. In addition, soft lithography of the microcontact printing technique was combined with the process of diblock copolymer micelles to produce micropatterns of nanoparticles. As an ink of the microcontact printing process, a single-layered film of diblock copolymer micelles was spin-coated directly onto the stamp and then transferred on the substrate by stamping. Formation of a single layer of nanoparticles in the micropattern was carried out by plasma treatment.

Variations of the lamellar period in thin films of diblock copolymers by selective staining agents

We investigated variations of the domain period of block copolymers by selective staining agents that are used for contrast enhancement in transmission electron microscopy. Employing thin films of symmetric diblock copolymers, homogeneous but selective staining was obtained throughout the film. Moreover, the thin film had a multilayered structure of parallel lamellae with the total film thickness quantized in terms of the lamellar period so that increments of the lamellar period by staining were conveniently and quantitatively evaluated as a function of staining time. In the case of a chemisorbed staining agent of osmium tetroxide for polybutadiene, the lamellar period in thin films of polystyrene-block-polybutadiene was gradually increased with staining time and had 22% increase at the saturation. Similar results were also obtained in the case of thin films of polystyrene-block-poly(methyl methacrylate) by ruthenium tetroxide and polystyrene-block-polyvinyl-pyridine by iodine.

FITD Simulation of Terahertz Near-Field Microscopes

The spatial resolutions of conventional THz TDS systems are limited by diffraction. In this work, we present a numerical analysis of apertureless THz pulse near-field microscopy (NFM), and successfully demonstrate that the THz NFM can have nanometer-scale resolution. For the numerical analysis we used CST MWS, a commercial software based on finite integral time domain (FITD) method. It is found that the THz near field is strongly localized around the probe tip as expected, which is of importance for nanometer resolution.